Electrostatic MEMS devices typically have at least one variable capacitor formed by two opposed plates. Many types of such MEMS devices operate most effectively when the spacing between the two plates is substantially uniform. Capacitive micromachined ultrasonic transducers (“CMUTs”) are a good example of this phenomenon.
Maintaining uniform spacing is especially challenging, however, when using conventional micromachining techniques. Specifically, sacrificial release processes commonly used in micromachining technologies often yields irregular spacing between the CMUT capacitor plates. The art has responded to this problem by fabricating CMUTs with very uniform and expensive silicon-on-insulator wafers (“SOI wafers”). Undesirably, however, this process wastes much of the SOI wafer, undesirably increasing fabrication costs.